Indirectly heated cathode



Jan. 31, 1939. G. J. IMBODEN INDIRECTLY HEATED CATHODE Filed March 29, 1957 BY a ATTORNEY Patented Jail. 31, 1939 PATENT OFFICE 7 2,145,833 lNDIRECTLY HEATEDCATHO-DE George J. Imboden, Emporium, Pa., assignor to Hygrade Sylvania Corporation, Salem, Mass., a corporation of Massachusetts Application March 29, 1937-, Serial No. 133,541

' 4 Claims. (015250-275 This invention relates to electron discharge 7 tubes and more particularly to such tubes as employ electron emitters'ofthe indirectly heated or unipotential type.

A principal object of the invention is to provide an improved structure of indirectly heated cathode for radio tubes and the like.

. Afeature of the invention relates to an indirectly heated cathode which is specially shaped to prevent it slipping, turning or changing its spacial relation with respect to the remaining electrodes of a tube mount. f

Another feature relates to an indirectly heated cathode which is particularly well-suited for 15 usewith a s-urrounding electrode such as a control grid or plate of flattened helical or tubular form. I p

'A further feature relates to a specially shaped cathode sleeve for indirectly heated cathodes 20 having a connectortab fastened thereto in such a position as to avoid the necessity of employing I a notched circular perforation in the'usual mica or ceramic insulator spacer.

. Other features and advantages not specifically 25 enumerated will be apparent after a consideration of the following detailed descriptions and 7 the appended claims.

While the invention will be illustrated herein 'as embodied in an electron discharge tube of the 30 triode "type, it will be understood that this is done merely for explanatory purposes and not 7 by way of limitation. Accordingly in the draw- "Fig. 1 is an elevational view, partly in section,

35 of atypical radio tube mount embodying the ,1 Fig. 6 represents a modification of the invention. I

Referring to Fig. 1, thenumeral I represents in dotted outline any well-known form of enclosing envelope such as customarily employed 5 in radio tubes and thelike and while the draw- {"ing shows an envelope of the glass type, it will be understood that a metal envelope may be I employed. Sealed into the envelope is any wellknown form of radio tube mount comprising the 55 stem or base 2 wherein. are sealed the various lead-in and support wires to I I inclusive. Supported on the wires 5 and II is the anode I2, preferably, although not necessarily, in the form of a flattened tubular member of metal, graphite, carbon or the like. Supported on the wires 6 5 and I0 isthe grid electrode I3 which may be of any well-known foraminous structure and merely for purposes of illustration it is shown in the drawing in the form of a fine helically wound wire supported on and attached to the grid side rods I4, I5.

Coaxially disposed within both the grid and plate is an indirectly heated cathode according to the invention which cathode is indicated generally by the numeral I6. Supported within the 5 cathode and suitably insulated therefrom is any well-known form of heater wire the free ends of which are connected to the wires 1 and 9. For the purpose of making electrical connection to the emissive coating on the cathode there is provided a metal tab I! which is connected to the Wire 8. In order to maintain the spacial positions of the various electrodes there are provided upper and lower insulator spacer members I 8 and I9 respectively, these members being of any suitable insulation material. Preferably, althoughno-t necessarily, members I8 and I9 are of mica sheets or discs having the necessary perforations to receive the ends of the various side rods and also the ends of the cathode, it being understood that the-mica discs are held in place on the wires 5 and II by metal tabs, eyelets or similar means fastened to the said wires.

In accordance with the invention the cathode comprises a metal sleeve of nickel or other similar metal having a cylindrical portion 2|] at its upper end and a similar cylindrical portion 2| at its lower end. The intervening part of the metal sleeve is flattened to provide a periphery having the same general shape as the shape of the grid I3 and of the plate I2 as shown more clearly in Fig. 2. The flattening of the major length of the sleeve results in the forming of upper and lower shoulders 22, 23 which are adapted to en,- gage the mica members I8 and I9 respectively so that the said sleeve is firmly held between the said mica members and is prevented from shifting vertically. Each of the mica members is provided with a circular perforation to accommodate the cylindrical ends of the sleeve. As indicated in Fig. 4, the cathode tab I! is disposed within the cylindrical portion H to which it may be welded, consequently both the upper and lower mica spacers may be perforated in an identical manner. Heretofore it has been the 5d usual practice to weld the tab IT to the outerface of the cathode sleeve thus necessitating the provision of a circular perforation in the lower mica the edge of the perforation requiring a notch to accommodate the tab. This notching of the mica not only increased the cost of fabricating the mica but required two separate kinds of micas, namely those for the top of the mount and those for the bottom of the mount. The flattened part of the cathode is provided with an electron emissive coating 24 of known materials.

Preferably, although not necessarily, the perforation in the mica. to receive the. cathode, is provided with two diametrically disposed notches or slots 24a so that part of the flattened shoulder 22 may project therethrough as indicatedin. .Fig. 3a., thus preventing the cathode sleeve from turning about its vertical axis. If desired, the slots 24 may be sufliciently long to permit the mica to pass beyond the shoulders 22. This latter arrangement while it prevents: turning of the cathode sleeve does not permit the mica to prevent longitudinal movementof the sleeve.

The particular shape of the cathode as shown not only improves the electrical characteristics.

of the tube by having the emitting surface cor.- respond to the shape of the grid l3, but it also reduces the cost of manufacture of. the tube and also reduces the percent of rejects. from the fact that the assembly or. threading of the sleeve into the mica spacers merely requires the insertion of the cylindrical ends, and the shoulders 22, 23 positively prevent the micas coming in contact with the emissive coating during the threading operation. Furthermore. the shoulders 22, 23 positively space the micas from the end turns of the grid and serve as means for accurately spacing the mica members vertically apart.

Various changes and modifications may be made herein without departing from thespirit and scope of the invention.

Thisresults.

Thus instead of flattening the main length of the cath'ode sleeve,.

and through which slot the said end protrudes. The mica 21 therefore engages the shoulder 29 on the cathode sleeve to prevent vertical movement of the cathode, and the flattened end 25 prevents turning movement of the cathode. It will beunderstood of course that the flattened portions 25 of the cathode sleeve may be provided. ateither or both ends.

What I claim is:

1. A radio tube mount comprising an indirectly heated cathode, a surrounding electrode for said cathode, said electrode having at least one side rod projecting beyond the ends thereof, a pair of insulator spacer members having aligned openingsto receive the ends of said cathode and said side rod, said cathode having cylindrical end portions joined to a flattened tubular portion the juncture of cylindrical portions and the tubular portiondeflning shoulders, and means for fastening said spacer members on said side-rod so that they abutagai-nst-said shoulders at opposite ends of the cathode, at least. one of'said spacers having a circular opening to receive a cylindrical end of the cathode, said opening also having lateral notches to receive partofthe flattened tubular portion of the cathode to restrain the cathode against turning movement.

2. A- radio tube mount according to claim 1 in which a connector tab is fastened to the inner faceof the lower cylindrical end portion of the cathode, and both said spacer members are provided with the same shape perforations.

3; A radio tube mount including an indirectly heated cathode having the major part of its length formed to a flattened tubular shape and terminating in at least one cylindrical end, a coating of electron-emissive material on said flattened: portion, and a mica spacer disc having a perforation with a circular portion and two oppositely disposed notches, said disc being assembled over the cathode so that the cylindrical endof the cathode passes through said circular portion and at least part ofsaid flattened section of the cathode registers with said notches to restrain said cathode againstturning movement with respect to the disc.

4. A mount according to claim 3 in which a metal tab is fastened to the'inner face of said cylindrical end of the cathodeso as to lie entirely 

